KR20120123265A - Oct device - Google Patents

Abstract

The photodetector PS of the OCT device is made of a semiconductor of the first conductivity type, has a first main surface 1a and a second main surface 1b facing each other, and is second to the first main surface 1a. A silicon substrate 1 having a conductive semiconductor layer 3 formed thereon, and a charge transfer electrode 5 provided on the first main surface 1a to transfer generated charges. On the silicon substrate 1, an accumulation layer 11 of the first conductivity type having a higher impurity concentration than the silicon substrate 1 is formed on the side of the second main surface 1b, and the second main surface 1b. Irregular irregularities 10 are formed in at least a region opposite to the semiconductor region 3 in. The area | region in which the irregular unevenness | corrugation 10 was formed in the 2nd main surface 1b of the silicon substrate 1 is optically exposed.

Description

OCT device {OCT DEVICE}

The present invention relates to an OCT device.

OCT (Optical Coherence Tomography) apparatus is an interferometer using low coherence light. The OCT apparatus can detect the intensity distribution of the reflected or scattered light as a tomographic image at the position specified by the position resolution of the coherence length with respect to the traveling direction of the light. An OCT apparatus is used for diagnosis of eyeballs, teeth, etc., for example. Patent Document 1 describes a technique using an OCT device for ophthalmic diagnosis. In the OCT device described in Patent Document 1, a light source that outputs light in the wavelength of the near infrared region is used, and a CCD (Charge Coupled Device: charge) is used as a light detector for detecting light in the wavelength of the near infrared region. Coupling element) An imaging element is used.

Patent Document 1: Japanese Patent Publication No. 2009-0344

In a CCD image pickup device, a silicon substrate which is generally cheap and easy to manufacture is used. However, in a CCD image pickup device using a silicon substrate, sensitivity rapidly deteriorates in a wavelength band of 900 nm or more. It is possible to maintain the sensitivity at around 1000 nm by thinning the silicon substrate, but there is a fear that an etalon phenomenon may occur. The etalon phenomenon is a phenomenon in which an incident detected light interferes with an incident light to be detected and reflected light from a surface opposite to the incident surface. For this reason, the etalon phenomenon affects the detection characteristic in the near infrared wavelength band.

An object of the present invention is to provide an OCT device having a photodetector having a sufficient sensitivity characteristic in a near infrared wavelength band while using a silicon substrate.

An OCT apparatus according to the present invention includes a light source for outputting light, a branching part for splitting the light output from the light source to output the first and second branching light, and a first branching light output from the branching part. The probe unit which irradiates the object to be measured and inputs and guides the light from the object to be measured and the light guided and reached by the probe unit are input as sample light, A combining unit for inputting the output and arriving second branched light as reference light, combining the input reference light and sample light, and outputting interference light by the combined wave; A photo detector is provided for detecting the intensity of the interference light output from the combining unit. The photo detector is made of a semiconductor of a first conductivity type, and has a first main surface and a second main surface facing each other. Of the second conductivity type on the first principal plane side. The silicon substrate in which the conductor area | region was formed, and the transfer electrode part which is provided on the 1st main surface of a silicon substrate, and transfers the electric charge which generate | occur | produced, The silicon substrate has the 1st conductivity type which has impurity concentration higher than a silicon substrate in a 2nd main surface side In addition to the formation of the accumulation layer, irregular irregularities are formed in a region facing at least the second conductivity type semiconductor region on the second main surface, and regions where irregular irregularities are formed in the second main surface of the silicon substrate , Optically exposed.

In the OCT apparatus according to the present invention, irregular irregularities are formed in a region of the silicon substrate that the photodetector has at least in the region facing the semiconductor region of the second conductivity type on the second main surface. For this reason, the interfering light incident on the photodetector is reflected, scattered, or diffused in the region, and travels a long distance in the silicon substrate. As a result, most of the interference light incident on the photodetector is absorbed by the silicon substrate without passing through the photodetector (silicon substrate). Therefore, in the said photodetector, the traveling distance of the interference light which injected into the photodetector becomes long, and also the distance which an interference light is absorbed becomes long. As a result, the sensitivity characteristic in the near infrared wavelength band is improved.

An accumulation layer of a first conductivity type having an impurity concentration higher than that of the silicon substrate is formed on the second main surface side of the silicon substrate. For this reason, the unnecessary carrier which generate | occur | produces irrespective of light on the 2nd main surface side is recombined, and dark current can be reduced. The accumulation layer of the first conductivity type suppresses trapping of carriers generated by interference light in the vicinity of the second main surface of the silicon substrate on the second main surface. For this reason, the carrier which generate | occur | produced by the interference light moves to the pn junction part of a 2nd conductivity type semiconductor region and a silicon substrate efficiently, and can improve the light detection sensitivity of a photodetector.

In the OCT device according to the present invention, the silicon substrate may have a portion corresponding to the second conductivity type semiconductor region to be thinner than the second main surface side, leaving a peripheral portion of the portion. In this case, a semiconductor photodetecting device can be obtained in which the first main surface and the second main surface side of the silicon substrate are respectively light incident surfaces.

In the OCT apparatus according to the present invention, the thickness of the accumulation layer of the first conductivity type may be larger than the height difference of irregular irregularities. In this case, as described above, the effect by the accumulation layer can be ensured.

In the OCT apparatus according to the present invention, the thickness of the silicon substrate may be set to be equal to or less than the pixel pitch. In this case, generation of cross talk between pixels can be suppressed.

According to the present invention, it is possible to provide an OCT device having a photodetector having a sufficient sensitivity characteristic in a near infrared wavelength band while using a silicon substrate.

1 is a schematic configuration diagram showing an OCT device.
2 is a perspective view showing a light detector.
3 is a view for explaining the cross-sectional configuration of the photo detector.
4 is a perspective view illustrating a modification of the photodetector.
5 is a view for explaining a manufacturing method of the photodetector.
6 is an SEM image of irregular irregularities formed on a p-type semiconductor substrate.

EMBODIMENT OF THE INVENTION Hereinafter, preferred embodiment of this invention is described in detail with reference to an accompanying drawing. In addition, in description, the same code | symbol is used for the same element or the element which has the same function, and the overlapping description is abbreviate | omitted.

First, with reference to FIG. 1, the structure of the OCT apparatus 100 is demonstrated. 1 is a schematic configuration diagram showing an OCT device. The OCT apparatus 100 has a structure for forming the tomographic image of the fundus of the eye to be examined, for example.

The OCT device 100 divides the low coherence light into a reference light and a signal light, and generates an interference light by superimposing the signal light passing through the fundus of the eye to be examined and the reference light passing through the reference object. To detect this. The detection result (detection signal) is input to an operation control device (not shown). The operation control device analyzes the detection signal to form a tomographic image of the fundus (particularly the retina).

The low coherence light source 102 is comprised by the broadband light source which outputs the low coherence light L0. As the low coherence light source 102, for example, a super luminescent diode (SLD: Super? Luminescent Diode) or a light emitting diode (LED: Light Emitted Diode) is used. The low coherence light L0 includes light having a wavelength in the near infrared region and has a temporal coherence length of about several tens of micrometers. The low coherence light L0 has a wavelength longer than the illumination light (wavelength of about 400 nm to 800 nm) of the fundus camera unit 101, for example, in a range of about 800 to 1100 nm.

The low coherence light L0 output from the low coherence light source 102 is guided through the optical fiber 104 to the optical coupler 106 (branch and coupler). The optical fiber 104 is composed of, for example, single-mode fiber or PM fiber (Polarization-Maintaining-Fiber: polarization plane holding fiber). The optical coupler 106 branches the low coherence light L0 into the reference light LR (second branched light) and the signal light LS (first branched light). The optical coupler 106 acts as both a means for splitting light (splitter) and a means for overlapping light (coupler: Coupler), but it is conventionally referred to as "optical coupler".

The reference light LR is guided by the optical fiber 108 and is emitted from the fiber cross section. The optical fiber 108 is composed of a single mode fiber or the like. The reference light LR becomes a parallel light beam by a collimator lens 110 and is reflected by the reference mirror 116 via the glass block 112 and the concentration filter 114.

The reference light LR reflected by the reference mirror 116 is again focused on the fiber cross section of the optical fiber 108 by the collimator lens 110 via the density filter 114 and the glass block 112, Guided to optical coupler 106 through optical fiber 108. The glass block 112 and the concentration filter 114 are delay means for matching the optical path distance (optical distance) of the reference light LR and the signal light LS, and also provide dispersion characteristics of the reference light LR and the signal light LS. It serves as a dispersion compensation means for fitting.

The density filter 114 also functions as a photosensitive filter for reducing the amount of light of the reference light, and is constituted by, for example, a rotary ND (Neutral Density) filter. The density filter 114 is rotated by a density filter drive mechanism (not shown), thereby changing the amount of reduction in the amount of light of the reference light LR. This adjusts the amount of light of the reference light LR that contributes to the generation of the interference light LC.

The reference mirror 116 is movable in the advancing direction of the reference light LR (both arrow directions shown in FIG. 1). Thereby, according to the eye axis length of the eye to be examined E, the working distance (distance between the objective lens 101a in the fundus camera unit 101 and the eye to be examined E), etc., The optical path distance is secured. By moving the reference mirror 116, an image of any depth position of the fundus can be acquired. The reference mirror 116 is moved by a reference mirror drive mechanism (not shown).

The signal light LS generated by the optical coupler 106 is guided to the end of the connection line 120 by the optical fiber 118. The optical fiber 118 is formed of a single mode fiber or the like. The optical fiber 120a is conductive inside the connection line 120. The optical fiber 118 and the optical fiber 120a may be formed of a single optical fiber, or may be formed integrally by joining the respective cross sections.

The signal light LS is guided into the connection line 120 and guided to the fundus camera unit 101 (probe unit). The signal light LS is irradiated from the fundus camera unit 101 (the objective lens 101a) to the eye E. The fundus camera unit 101 is used to photograph a color image, a black and white image or a fluorescent image on the fundus surface. The fundus camera unit 101 includes an illumination optical system and a photographing optical system similarly to a conventional fundus camera.

The signal light LS incident on the eye E is formed and reflected on the fundus. At this time, the signal light LS not only reflects from the surface of the fundus but also reaches the deep region of the fundus and is scattered at the refractive index boundary. Therefore, the signal light LS via the fundus contains information reflecting the surface form of the fundus and information reflecting the backscattering state at the refractive index boundary of the deep tissue of the fundus. This light is only referred to as "fundular reflection light of signal light LS".

The fundus reflected light (sample light) of the signal light LS travels in the path in the fundus camera unit 101 in the reverse direction and is focused on the end face of the optical fiber 120a, thereby connecting the connection line 120 and the optical fiber 118 to each other. Return to the optocoupler 106 through.

The optical coupler 106 generates the interference light LC by superimposing the signal light LS returned via the eye E and the reference light LR reflected by the reference mirror 116. The interference light LC is guided to a spectrometer 124 through the optical fiber 122. The optical fiber 122 is composed of a single mode fiber or the like. In the present embodiment, a Michelson type interferometer is used, but an interferometer of any type such as a Mach-Zender type can be used.

The spectrometer (spectrometer) 124 includes a collimator lens 126, a diffraction grating 128, an imaging lens 130, and a photodetector PS. The diffraction grating 128 may be a transmission diffraction grating which transmits light, or may be a reflection diffraction grating which reflects light.

The interference light LC incident on the spectrometer 124 becomes a parallel light beam by the collimator lens 126 and is spectroscopically (spectral resolved) by the diffraction grating 128. The spectroscopic interference light LC is imaged on the imaging surface of the photodetector PS by the imaging lens 130. The photodetector PS detects each spectrum of the spectroscopic interference light LC, converts it into an electrical signal, and outputs the detected signal to an operation control device (not shown). The detection signal is a signal corresponding to the intensity of each spectrum of the spectroscopic interference light LC. An arithmetic and control device analyzes the detection signal input from the photodetector of the OCT apparatus 100, and forms the tomographic image of the fundus of the eye to-be-E.

Next, the photodetector PS is demonstrated with reference to FIG. 2 and FIG. 2 is a perspective view showing a light detector. 3 is a view for explaining the cross-sectional configuration of the photodetector.

As shown in FIG. 2, the photodetector PS is a back-side incident solid-state image pickup device, and is a BT-CCD (charge-coupled device) obtained by etching the back side of the semiconductor substrate SS with an aqueous KOH solution or the like. )to be. The recessed part TD is formed in the center area | region of the etched semiconductor substrate SS, and the thick frame part exists around the recessed part TD. The side surface of the recessed portion TD is inclined at an obtuse angle with respect to the bottom surface BF. The thinned central region of the semiconductor substrate SS is a light sensitive region (imaging region). The interference light LC enters the light sensitive region along the negative direction of the Z axis. The bottom surface BF of the recessed portion TD of the semiconductor substrate SS constitutes a light incident surface. It is also possible to make photodetector PS into the back-incidence type solid-state image sensor with which the whole area was thinned.

The photodetector PS is equipped with the p-type semiconductor substrate 1 as the said semiconductor substrate SS. The p-type semiconductor substrate 1 is made of silicon (Si) crystal and has a first main surface 1a and a second main surface 1b facing each other. The thickness of the p-type semiconductor substrate 1 is set to the pixel pitch P or less. In this embodiment, the pixel pitch P is about 10-48 micrometers, and the thickness of the p-type semiconductor substrate 1 is about 10-30 micrometers. In this embodiment, an example of two-phase clock driving is shown, and under each transfer electrode, there are regions (not shown) in which impurity concentrations are different in order to ensure one-way transfer of charge. .

On the first main surface 1a side of the p-type semiconductor substrate 1, an n-type semiconductor layer 3 as a charge transfer portion is formed, and between the p-type semiconductor substrate 1 and the n-type semiconductor layer 3 The pn junction is formed. On the first main surface 1a of the p-type semiconductor substrate 1, a plurality of charge transfer electrodes 5 as transfer electrode portions are provided with an insulating layer 7 interposed therebetween. Although not shown, an isolation region for electrically separating the n-type semiconductor layer 3 for each vertical CCD is also formed on the first main surface 1a side of the p-type semiconductor substrate 1. The thickness of the n type semiconductor layer 3 is about 0.5 micrometer.

Irregular irregularities 10 are formed in the entire photosensitive region 9 on the second main surface 1b of the p-type semiconductor substrate 1. The accumulation layer 11 is formed in the 2nd main surface 1b side of the p-type semiconductor substrate 1, and the 2nd main surface 1b is optically exposed. The optical exposure of the second main surface 1b includes the case where the second main surface 1b is not only in contact with an atmospheric gas such as air, but also an optically transparent film is formed on the second main surface 1b. do. In the case where the photodetector PS is a backside incident type solid-state imaging device in which the entirety is thin, irregular irregularities 10 may be formed over the entire second main surface 1b of the p-type semiconductor substrate 1. When the photodetector PS is a back-incident type solid-state image sensor thinned only in the vicinity of the photosensitive region 9, the p-type semiconductor substrate 1 also includes an inclined surface that reaches the unframed peripheral frame portion or frame portion. Irregular unevenness 10 may be formed over the entire second main surface 1b.

The entire backside incident type solid-state imaging device can be obtained by attaching a separate substrate to the surface of the semiconductor substrate SS without providing a frame portion, and then polishing the back surface side of the semiconductor substrate SS. As shown in FIG. 4, in the photodetector PS ₁ , the entire back side of the semiconductor substrate SS is thinned. In the photodetector PS ₁ , irregular irregularities 10 are formed on at least the region corresponding to the photosensitive region on the back surface (second main surface) of the semiconductor substrate SS. The accumulation layer (not shown) mentioned above is formed in the back surface side of the semiconductor substrate SS.

Next, the manufacturing method of the photodetector PS of this embodiment is demonstrated.

First, a p-type semiconductor substrate 1 having a first main surface 1a and a second main surface 1b facing each other is prepared. The thickness of the p-type semiconductor substrate 1 to be prepared is about 300 μm, and the specific resistance is about 0.001 to 10 kΩ · cm. In the present embodiment, "high impurity concentration" means that the impurity concentration is, for example, about 1x10 ¹⁷ cm ^-3 or more, and "+" is added to the conductive type. "Low impurity concentration" shows impurity concentration of about 1 * 10 <^15> cm <^-3> or less, and attaches "-" to a conductive type. Examples of the n-type impurity include antimony (Sb) and arsenic (As), and examples of the p-type impurity include boron (B) and the like.

Next, the n-type semiconductor layer 3 is formed on the first main surface 1a side of the p-type semiconductor substrate 1. The n-type semiconductor layer 3 is formed by diffusing n-type impurities from the first main surface 1a side in the p-type semiconductor substrate 1.

Next, the p-type semiconductor substrate 1 is thinned as described above from the second main surface 1b side.

Next, the accumulation layer 11 is formed on the second main surface 1b side of the p-type semiconductor substrate 1. As in the above-described embodiment, the accumulation layer 11 has ion such that the p-type impurity is higher than the p-type semiconductor substrate 1 in the p-type semiconductor substrate 1 from the second main surface 1b side. It is formed by infusion or diffusion. The thickness of the accumulation layer 11 is about 0.5 micrometer, for example. The accumulation layer 11 may be formed before the irregular unevenness 10 is formed, or may be formed after the irregular unevenness 10 is formed.

Next, the p-type semiconductor substrate 1 is heat treated to activate the accumulation layer 11. Heat treatment, for example, under the atmosphere as N ₂ gas, in the range of about 800 ~ 1000 ℃, carried out over a period of about 0.5 to 1.0 hours. At this time, the crystallinity of the p-type semiconductor substrate 1 is also restored.

Next, pulse laser light PL is irradiated to the second main surface 1b side of the p-type semiconductor substrate 1 to form irregularities 10. Here, as shown in FIG. 5, after arranging the p-type semiconductor substrate 1 in the chamber C, the pulsed laser light PL from the pulse laser generator PLD disposed outside the chamber C is shown. ) Is irradiated to the p-type semiconductor substrate 1. The chamber C has a gas inlet G _IN and a gas outlet G _OUT . In the chamber C, an inert gas flow G _f is introduced by introducing an inert gas (for example, nitrogen gas, argon gas, etc.) from the gas inlet G _IN and discharged from the gas outlet G _OUT . Formed. Dust generated when the pulsed laser light PL is irradiated is discharged out of the chamber C by the inert gas flow G _f to prevent adhesion of processed powder or dust to the p-type semiconductor substrate 1. Doing.

In this embodiment, a picosecond-femtosecond pulse laser generator is used as a pulse laser generator PLD, and a picosecond-femtosecond is spread over the whole surface of the 2nd main surface 1b. Pulsed laser light is irradiated. The second main surface 1b is damaged by picosecond to femtosecond pulsed laser light, and as shown in FIG. 6, irregular irregularities 10 are formed on the front surface of the second main surface 1b. The irregular concave-convex 10 has a surface crossing with respect to the direction orthogonal to the 1st main surface 1a. The height difference of the unevenness | corrugation 10 is about 0.5-10 micrometers, for example, and the space | interval of the convex part in the unevenness | corrugation 10 is about 0.5-10 micrometers. The pulse time width of picosecond to femtosecond pulsed laser light is, for example, about 50 fs to 2 ps, the intensity is about 4 to 16 GW, and the pulse energy is about 200 to 800 μJ / pulse, for example. . More generally, the peak intensity is 3 x 10 ¹¹ to ^2.5 x 10 ¹³ (W / cm ² ), and the fluence is about 0.1 to 1.3 (J / cm ² ). 6 is an SEM image of observing irregular irregularities 10 formed on the second main surface 1b.

Next, the p-type semiconductor substrate 1 is heat treated. Heat treatment, for example, under an atmosphere that the N ₂ gas, in the range of about 800 ~ 1000 ℃, is carried out over a period of about 0.5 to 1.0 hours. By the heat treatment, crystal damage can be recovered and recrystallized in the p-type semiconductor substrate 1, and problems such as dark current increase can be prevented. The heat treatment after the formation of the accumulation layer 11 may be omitted, and only the heat treatment after the irregular unevenness 10 is formed.

Next, the insulating layer 7 and the charge transfer electrode 5 are formed. Processes for forming the insulating layer 7 and the charge transfer electrode 5 are already known, and description thereof is omitted. The charge transfer electrode 5 is made of polysilicon or metal, for example. The insulating layer 7 is made of SiO ₂ , for example. A protective film may be further formed to cover the insulating layer 7 and the charge transfer electrode 5. The protective film is made of, for example, BPSG (Boron Phosphor Silicate Glass). This completes the photodetector PS.

In the photodetector PS, when the interference light LC enters from the light incident surface (second main surface 1b), irregular irregularities 10 are formed on the second main surface 1b, and thus the incident interference light is incident. (LC) is scattered by the unevenness 10 and progresses in the p-type semiconductor substrate 1 in various directions. The light component which reaches the 1st main surface 1a etc. advances in various directions by the diffusion in the unevenness | corrugation 10. As shown in FIG. For this reason, the possibility that the light component which reached | attained the 1st main surface 1a etc. totally reflects on the 1st main surface 1a is extremely high. The light component totally reflected on the first main surface 1a or the like repeats total reflection on the other surface, reflection, scattering, or diffusion on the second main surface 1b, and the running distance becomes longer. In this way, the interference light LC incident on the photodetector PS is reflected, scattered, or diffused in the unevenness 10 and travels a long distance in the p-type semiconductor substrate 1. Then, the interference light LC incident on the photodetector PS is absorbed by the p-type semiconductor substrate 1 while traveling the inside of the p-type semiconductor substrate 1 for a long distance, and is applied to the interference light LC. The resulting carriers become charges for each pixel of the n-type semiconductor layer 3, and are transferred and detected. Therefore, in the photodetector PS, the sensitivity characteristic in the near-infrared wavelength band improves.

By the way, when regular unevenness | corrugation is formed in the 2nd main surface 1b, although the light component which reaches | attains the 1st main surface 1a and the side surface is diffused by unevenness | corrugation, it progresses in the same direction. For this reason, the possibility that the light component which reached | attained the 1st main surface 1a or the side surface totally reflects on the 1st main surface 1a or the side surface becomes low. And the light component which permeate | transmits on the 1st main surface 1a, the side surface, and the 2nd main surface 1b increases, and the running distance of the interference light LC which injected into the photodetector PS will become short. As a result, it becomes difficult to improve the spectral sensitivity characteristic in the near infrared wavelength band.

In the photodetector PS, cross talk between pixels may occur due to reflection, scattering, or diffusion due to the unevenness 10, and the resolution may be lowered. However, since the thickness of the p-type semiconductor substrate 1 is set to the pixel pitch P or less, the photodetector PS can suppress the occurrence of crosstalk between the pixels.

In the photodetector PS, the accumulation layer 11 is formed in the 2nd main surface 1b side of the p-type semiconductor substrate 1. Thereby, the unnecessary carrier which generate | occur | produces irrespective of light on the 2nd main surface 1b side is recombined, and dark current can be reduced. The accumulation layer 11 suppresses trapping of carriers generated by light in the vicinity of the second main surface 1b on the second main surface 1b. For this reason, the carrier which generate | occur | produced by the interference light LC can move efficiently by pn junction, and can further improve the photodetection sensitivity of the photodetector PS.

In this embodiment, the p-type semiconductor substrate 1 is heat-treated after the accumulation layer 11 is formed. As a result, the crystallinity of the p-type semiconductor substrate 1 is restored, and problems such as an increase in dark current can be prevented.

In the present embodiment, after the p-type semiconductor substrate 1 is heat treated, the charge transfer electrode 5 is formed. Thus, even when a material having a relatively low melting point is used for the charge transfer electrode 5, the charge transfer electrode 5 is unlikely to melt by the heat treatment, and the charge transfer electrode 5 is not affected by the heat treatment. Can be appropriately formed.

In the present embodiment, irregular picoseconds 10 are formed by irradiating picosecond to femtosecond pulsed laser light. Thereby, the irregular unevenness | corrugation 10 can be formed suitably and easily.

By the way, in a semiconductor photodetecting device called a solid-state imaging device, by setting the semiconductor substrate made of silicon thick (for example, about 200 µm), it is possible to realize a semiconductor photodetecting device having a spectral sensitivity characteristic in a near infrared wavelength band. Do. However, when the thickness of the semiconductor substrate is increased, in order to obtain good resolution, it is necessary to apply a high bias voltage of about several tens of volts to completely deplete the semiconductor substrate. This is because if the neutral region is not partially depleted and the neutral region remains partially in the semiconductor substrate, carriers generated in the neutral region diffuse and the resolution is prevented from deteriorating.

If the semiconductor substrate is thick, the dark current also increases. For this reason, it is also necessary to cool a semiconductor substrate (for example, -70-100 degreeC), and to suppress dark current increase.

However, in the photodetector PS, as described above, since irregular irregularities 10 are formed on the second main surface 1b, the traveling distance of the interference light LC incident on the photodetector PS is long. Lose. For this reason, the photodetector PS which has sufficient spectral sensitivity characteristic in the near-infrared wavelength band can be implement | achieved without thickening the semiconductor substrate (p-type semiconductor substrate 1), especially the part corresponding to the photosensitive area | region 9. have. Therefore, the photodetector PS has a very low bias voltage applied or no bias voltage applied than a semiconductor photodetecting device having a spectral sensitivity characteristic in the near infrared wavelength band by thickening the semiconductor substrate. , Good resolution can be obtained. In addition, depending on the application, cooling of the semiconductor substrate is also unnecessary.

When the semiconductor substrate, especially the part corresponding to the photosensitive region, is thinned, an etalon phenomenon may occur. The etalon phenomenon is a phenomenon in which interference between the detected light incident from the back surface and the light detected by the incident light is reflected from the surface and affects detection characteristics in the near infrared wavelength band. However, in the photodetector PS, since the irregular unevenness | corrugation 10 is formed in the 2nd main surface 1b, the light reflected by the unevenness | corrugation 10 with respect to the phase of incident light has the phase difference which distributed. As a result, these lights cancel each other out, and the etalon phenomenon is suppressed.

In the present embodiment, the p-type semiconductor substrate 1 is thinner than the second main surface 1b side. Thereby, the semiconductor photodetecting element which made the 1st main surface 1a and the 2nd main surface 1b side of the p-type semiconductor substrate 1 into the light incident surface, respectively, can be obtained. That is, the photodetector PS can be used not only as a back surface incident type solid-state image sensor, but also as a surface incident type solid-state image sensor.

After the accumulation layer 11 is formed, when the laser beam is irradiated to form irregular irregularities 10, the thickness of the accumulation layer 11 is set to be larger than the height difference between the irregular irregularities 10. It is preferable. In this case, even if the irregular unevenness | corrugation 10 is formed by irradiating pulsed laser light, the accumulation layer 11 remains reliably. Therefore, the effect by the accumulation layer 11 can be ensured.

As mentioned above, although preferred embodiment of this invention was described, this invention is not necessarily limited to embodiment mentioned above, A various change is possible in the range which does not deviate from the summary.

The p-type and n-type conductive types in the photodetector PS according to the present embodiment may be changed so as to be opposite to those described above.

[Industrial Availability]

INDUSTRIAL APPLICABILITY The present invention can be used for an OCT device used for ophthalmologic diagnosis or dental diagnosis.

One … p-type semiconductor substrate 1a. First principal plane
1b. Second principal plane 3... n-type semiconductor layer
5 ... Charge transfer electrode 7. Insulating layer
9 ... Photosensitive region 10. Irregular irregularities
11 ... Accumulation layer 100.. OCT device
101. Fundus camera unit 102. Low coherence light source
106. Optocoupler 116. Reference mirror
124. Spectrometer E... Eye exam
PS, PS ₁ ... Photodetector SS... Semiconductor substrate
TD… Concave portion

Claims (4)

As an OCT device,
A light source for outputting light,
A branching unit which splits the light output from the light source and outputs first and second branched lights;
A probe unit for irradiating the first branched light output from the branching unit to the measurement target object and inputting and guiding light from the measurement target unit;
The light guided and reached by the probe unit is input as sample light, and the second branched light output from the branch unit is input as reference light, and these input reference light and sample are input. A combining unit for combining light and outputting interference light by the combining;
And a photo detector for detecting the intensity of the interference light output from the combining section,
The photo detector,
A silicon substrate comprising a first conductive semiconductor, having a first main surface and a second main surface facing each other, and having a second conductive semiconductor region formed on the first main surface;
It is provided on the first main surface of the silicon substrate and has a transfer electrode portion for transferring the generated charges,
In the silicon substrate, an accumulation layer of a first conductivity type having a higher impurity concentration than the silicon substrate is formed on the second main surface side, and the semiconductor region of at least a second conductivity type on the second main surface. Irregularities are formed in the area opposite to
An OCT device according to claim 2, wherein the irregularly formed regions of the irregularities in the second main surface of the silicon substrate are optically exposed. The method according to claim 1,
The silicon substrate is characterized in that the portion corresponding to the semiconductor region of the second conductivity type is thinner than the second main surface side leaving a peripheral portion of the portion. The method according to claim 1 or 2,
The thickness of the said accumulation layer of a 1st conductivity type is larger than the difference of the height of the irregularity which is irregular, The OCT apparatus characterized by the above-mentioned. The method according to any one of claims 1 to 3,
The said silicon substrate is set to the thickness below pixel pitch, The OCT apparatus characterized by the above-mentioned.

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